1. Field of the Invention
The present invention relates to an apparatus for depositing thin films on a wafer such as semiconductor substrate by continuous gas injection.
2. Description of the Related Art
Referring to FIG. 1, a conventional thin film deposition apparatus comprises a reaction gas transfer portion 100 for transferring a reaction gas into a reactor 200, and an exhaust portion 300 for exhausting the gas out of the reactor 200.
The reaction gas supply portion 100 comprises a first reaction gas supply portion 110 for supplying a first reaction gas to the reactor 200, a second reaction gas supply portion 120 for supplying a second reaction gas to the reactor 200, and an inert gas supply portion 130 for supplying an inert gas to the reactor 200. The exhaust portion 300 has an exhaust pump 310 for discharging the gas out of the reactor 200.
The gas supply portions 110, 120 and 130 and the exhaust pump 310 are connected by pipe lines having a plurality of on/off valves 111, 112, 113, 114, 115, 121, 122, 123, 124, 125, 131, 132, 133 and 134 which are controlled by a connector (not shown) connected to each of the valves.
The first reaction gas supply portion 110 includes a first source container 116 filled with a first liquid material as a source of the first reaction gas, and a mass flow controller (MFC) for controlling the flow of a transfer gas for transferring the first reaction gas to the reactor 200. The second reaction gas supply portion 120 includes a second source container 126 filled with a second liquid material as a source of the second reaction gas, and an MFC for controlling the flow of the transfer gas for transferring the second reaction gas to the reactor 200. The inert gas supply portion 130 comprises an inert gas container 136 for supplying the inert gas and an MFC for controlling the flow of the inert gas to the reactor 200.
In the thin film deposition apparatus having the above structure, for example, the valves 111, 112 and 113 are open, the transfer gas provided through a first supply line 11 and the valve 111 enters the reactor 200 together with the first reaction gas contained in the first source container 116 through the valves 112 and 113 and a first reactor pipe line 21.
Then, when the valves 114 and 115 are open, the transfer gas provided through the first supply line 11 is discharged through the valves 114 and 115, a first exhaust line 71 and the exhaust pump 310.
Then, when the valves 131, 132 and 134 are open, the inert gas flows into the reactor 200 through the first reactor pipe line 21 and a third reactor pipe line 23, so that the reaction gas remaining in the first reactor pipe line 21 and the reactor 200 is discharged.
Then, when the valves 132 and 134 are closed an) the valves 121, 122 and 123 are open, the transfer gas provided through a second supply line 12 and the valve 121 enters the reactor 200 together with the second reaction gas contained in the second source container 126 through the valves 122 and 123 and a second reactor pipe line 22.
However, when the valve 134 is closed in order to transfer another reaction gas to the reactor 200, the inert gas cannot be provided to the first reactor pipe line any more. Thus, the reaction gas remaining in the first reactor pipe line 21, not being discharged, is mixed with the next reaction gas. Also, when the valve 132 is closed, the reaction gas in a part of the reactor 200 near the exhaust line is not discharged, so that the remaining reaction gas is mixed with the next reaction gas.
On the other hand, when the valves are turned on/off in order to transfer another reaction gas, the internal pressure of the lines connected to the corresponding valves changes. Such a change in pressure means that a stable supply of the reaction gas is not certain and causes cavitation to the supply lines, so that the transfer of the reaction gas becomes difficult.